Fire detector



Feb. 15, 1966 T. N. VASSIL 3,235,860

FIRE DETECTOR Filed June 29, 1960 9 Sheets-Sheet 1 I /TI I r- 321 I v 4: I I is/ A: A/TPI I I 28 5 I I I l I I l I I I P2 3| I I 1 I I I I I =f/'27 1: Tpz I I 29 5E 35 I I 20 HAZARDOUS AREA Feb. 15, 1966 T. N. VASSIL 3,235,860

FIRE DETECTOR Filed June 29, 1960 9 Sheets-Sheet 2 Pl PIA 925 2 T. N. VASSIL FIRE DETECTOR Feb. 15, 1966 9 Sheets-Sheet 5 Filed June 29, 1960 FIG.4A

Feb. 15, 1966 'r. N. VASSIL 3,235,850

FIRE DETECTOR Filed June 29, 1960 9 Sheets-Sheet 4 T. N. VASSIL FIRE DETECTOR Feb. 15, 1966 Filed June 29, 1960 9 Sheets-Sheet 5 'l 3,4 I L -J /TPN-2 PHOTOCONDUCTOR FILTER F CADMIUM SELENIDE owmdmu out PIC-3.58

Zummw TPN-3 FIG.5A

WAVELENGTH IN MIC RONS Feb. 15, 1966 T. N. VASSIL 3,235,860

FIRE DETECTOR Filed June 29, 1960 9 Sheets-Sheet 6 s e s F I 7 T. N. VASSIL FIRE DETECTOR Feb. 15, 1966 9 Sheets-Sheet 7 Filed June 29, 1960 Feb. 15, 1966 1-. N. VASSIL 3,235,860

FIRE DETECTOR Filed June 29, 1960 9 Sheets-Sheet 9 FIG.I4

SQUIB TEST RESPONSE TEST MAIN @j TL RI. ML (AMBER) (RED) (GREEN) 58 MAIN TEST SWITCHES (BLUE) SWITCH LOW PRESSURE ALARM LP (WHITE) United States Patent Office 3,235,860 Patented Feb. 15, 1966 3,235,860 FIRE DETECTOR Theo N. Vassil, Flushing, N.Y., assignor to American District Telegraph Company, Jersey City, NJ., a corporation of New Jersey Filed June 29,1960, Ser. No. 39,528 14 Claims. (Cl. 340-223) The present invention relates to fire detectors and more particularly to fire detectors adapted especially for use with extremely hazardous and rapid burning materials.

In the handling and processing of explosives and other hazardous materials, peculiar fire protection requirements are encountered in view of the necessity for prompt remedial action upon the advent of a fire condition. In most fire protection situations, speed of detection is important, but usually a delay of many seconds or even minutes is tolerable. However, when handling or processing flamesensitive explosives and certain other hazardous materials, it is desirable that detection and remedial action be extremely prompt and preferably in a time interval of the order of a few milliseconds.

These requirements are perhaps most stringent when the materials involved are of the type in which combustion propagates at a high velocity and which include oxygen-supplying compounds, since with such materials, if an incipient fire is not detected and extinguished within an extremely short time interval, extinguishment will rapidly become impossible, or at least extremely diflicult. An example of such a material is a mixture of a flammable polymer, e.g., polyurethane or polybutadiene, and an oxygen-furnishing material, e.g., ammonium perchlorate. With such a material a fire cannot be smothered but must be extinguished by cooling to below the combustion temperature. For most practical purposes, such cooling will be impossible unless the cooling medium is brought into contact with the flame in a very short time. 500 milliseconds is sometimes considered an outside time limit for detection and application of the cooling medium, but in some cases even such a time interval may be too long. It is, of course, desirable to achieve these results in a much shorter time, and preferably a time of the order of a few milliseconds.

In the handling and processing of materials which are or may become explosive in the presence of flame, prompt detection and application of the extinguishing medium is desirable to minimize the explosion hazard, and again a time interval of the order of a few milliseconds is highly desirable.

In fire detection under the hazardous conditions con- I transient nature not be allowed to initiate a spurious detection of fire.

In accordance with the foregoing, a principal object of the invention has been the provision of a novel and improved fire detector.

More particularly, it has been a principal object of the p invention to provide such a detector which is especially adapted for use in protecting hazardous materials, in that the detection time is extremely short.

Still another object of the invention has been the provision of a fire detector which will produce a usable output signal in a time interval of the order of a few microseconds.

Another object of the invention has been the provision of a fire detector which will detect a fire condition and actuate an extinguishing system in a time interval of the order of a few milliseconds or less and which will result in application of an extinguishing medium to the fire in a very short time after detection.

A further object of the invention has been the provision of such a detector which will be highly resistant to spurious detection resulting from permanent or transient ambient conditions.

Still another object of the invention has been the provision of such a detector which will exhibit extreme reliability.

Yet another object of the invention has been the provision of a fire detector of the above type which is adapted for intermittent use and which may be tested fully prior to each use.

A further object of the invention has been the provision of a fire detector having multiple detecting units with partially overlapping detecting fields which will eliminate blind spots formed by masked areas on a surface to be protected.

Still a further object of the invention has been the provision of a fire detecting element having in association therewith a testing element which affords a realistic and reliable test of the integrity of the detecting element.

Another object of the invention has been the provision of a fire detecting and extinguishing system adapted to respond to a fire condition in a very short time interval, and which will bring a fire extinguishing medium into operative contact with an incipient fire within a total elapsed time interval of the order of a few milliseconds.

A feature of the invention has been the provision of a fire detector which produces virtually instantaneously a usable signal voltage upon the occurrence of a fire con dition in a protected area.

Another feature of the invention has been the provision of a fire detector of the above type which contains no moving parts.

Other and further objects, features and advantages of the invention will appear more fully from the following description.

The invention will now be described in detail with reference to the appended drawings, in which:

FIG. 1 is a schematic drawing illustrating one form of fire detecting and extinguishing system in accordance with the invention; I

FIG. 2 is a perspective View showing a typical installation of the fire detecting unit of FIG. 1;

FIG. 3 is a schematic drawing illustrating another form of fire detector in accordance with the invention employing multiple fire detecting units and having ambient compensating elements;

FIG. 4 is a perspective view showing a typical installation of the fire detecting units of FIG. 3;

FIG. 4A is a plan view illustrating the fields of view of the detecting units of FIG. 4;

FIG. 5 is a schematic drawing illustrating another form of fire detector in accordance with the invention;

FIG. 5A show s a modification of the circuit of FIG. 5;

FIG. 5B is a curve of typical response characteristics;

FIG. 6 is a longitudinal cross-sectional view illustrating one form of combined fire detecting element and test element in accordance with the invention;

FIG. 7 is a view similar to FIG. 6 illustrating a modified form of construction of a detecting and test element in accordance with the invention;

FIG. 8 is a view similar to FIG. 6 illustrating another modified form of construction of a detecting and test element in accordance with the invention;

FIG. 9 is a View similar to FIG. 6 illustrating still another modified form of construction of a detecting and test element in accordance with the invention;

FIG. 10 is a perspective view of the element of FIG. 9;

FIG. 11 is a longitudinal sectional view of yet another modified form of detecting and test elements in accordance with the invention;

FIG. 12 is an end view of the element of FIG. 11;

FIG. 13 is a schematic diagram illustrating a test circuit in accordance with the invention; and

FIG. 14 is an elevational view showing a typical test panel for the circuit of FIG. 13.

In the various figures of the drawings like reference characters denote like elements.

Referring now to the drawings, and more particularly to FIGS. 1 and 2, there is illusrated a simple form of system embodying the invention. The hazardous area to be protected is designated 20 and is shown in FIG. 2 as a material surface at or near the top of a cylindrical container 21. The container 21 is provided with upstanding brackets 22 and 23 which have mounted thereon detecting elements formed by photocells P1 and P2, respectively. The photocells P1 and P2 are mounted and adjusted so that the field of view of each is the entire surface area 20 with as little additional outside area as possible. The field of view of photocell P1 is outlined by lines PIA and P113 while that of photocell P2 is outlined by lines P2A and P2B. I

Each of the photcells views this hazardous area from a different horizontal position.v As shown, these positions are 180 apart, but different angular dispositions may be used so long as ambient illumination coming from a source in the surrounding area and impinging on one of the photocells is not likely to impinge on the other. It is contemplated that this ambient illumination may be permanent or transient, and may be reflected from the surface 20. An unpredictable glint of light reflected from the hazardous surface is perhaps the most likely source of a spurious alarm.

The term photocell as used herein is intended to designate the various forms of light-sensitive devices whose conductivity is altered when light contacts a pho tosensitive surface thereof. It is highly desirable but not necessary that the photocells used in the invention be of the solid state type, and preferably photoconductive cells or phototransistors.

Where a fire in the protected hazard has a predominant spectral energy frequency or band of frequencies, as will usually be the case, the photocells may be selected to produce a peak response at this frequency or band of frequencies. Moreover, an optical filter may be installed in front of each photocell to allow the predominant spectral energy frequency or band of frequencies of the protected hazard to pass and to inhibit the passage of other frequencies. When protecting a material such as the mixture of polyurethane and ammonium perchlorate mentioned above, spectral energy in the infrared range will tend to predominate, and photocells especially sensitive to this range (with or without optical filters) may be used to advantage. Photocells P1 and P2 might, for example, be cadmium selenide cells Whose response peaks in the infrared range at about 0.75 micron. Light energy incident thereon may with advantage be passed through an optical filter which cuts off spectral energy below about 0.7 micron.

The light-sensitive surfaces or cathodes of the photocells P1 and P2 are connected to a negative terminal 24 of a source of potential. For convenience the terms cathode and anode will be used in referring to the photocell electrodes as in the case of conventional photoelectric cells, although these terms are not necessarily properly used in connection with certain solid state devices. The anodes of photocells P1 and P2 are each coupled to positive terminal 25 through a respective one of resistors 26 and 27. The anode of photocell P1 is also connected to the base of a transistor T 1, while the anode of photocell P2 is connected to the base of a transistor T2. The emitters of transistors T1 and T2 are coupled to positive terminal 25 through a respective one of potentiometers 28 and 29. The collectors of transistors T1 and T2 are coupled to negative terminal 24 through a respective one of resistors 30 and 31.

The slider of poteniometer 28 is connected to the base of a power transistor TPl, while the slider of potentiometer 29 is connected to the base of a power transisttor TP2. The emitter-collector circuits of transistors TPl and TP2 are included in a series circuit extending from negative terminal 24 through a conductor 32, an explosive squib or primer 33, a conductor 34, the emitter-collector circuit of transistor TP1, the emitter-collector circuit of transistor TP2, and a rectifier 35 to positive terminal 25. This series circuit may conveniently .be termed the squib circuit.

The sliders of potentiometers 28 and 29 are normally adjusted so that under steady state conditions the emitter-base voltage of power transistors TF1 and TP2 will be insuifieient for these transistors'to conduct and hence current cannot flow through the series circuit including the squib 33. The diode 35 insures that current cannot flow through this series circuit in any event unless the voltage in the emitter-base circuits of the power transistors equals or exceeds the breakdown voltage of diode 35. Thus even though steady state ambient light conditions may be such that transistors TP1 and TP2 would be conditioned so as to be conductive, as will be explained below, the emitter-base voltages of those power transistors must reach a minimum or threshold value before conduction occurs, and this value is determined by the rating of diode 35.

Under steady state conditions, photocell P1 and resistor 26 act as a voltage divider setting the emitter-base voltage of transistor T1 to a value at which the current flow through potentiometer 28 produces the desired emitterbase voltage for transistor 'IPl. Photocell P2 and resistor 27 act similarly for transistors T2 and TP2.

Should light energy (photons) from a fire contact the light-sensitive surfaces of photocells P1 and P2, the electrical resistances of these photocells will drop. In general, the drop in resistance of the photocells will be proportional to the light energy incident thereon, and, if this light energy is from a fire in the direct field of view of the photocells, the drop in resistance will be appreciable.

The drop in resistance of photocell P1 will cause an increase in the voltage drop across resistor 26 (because photocell P1 and resistor 26 act as a voltage divider), while the drop in resistance of photocell P2 will cause a similar increase in the voltage drop across resistor 27. As a result, the emitter-base voltages of both transistors T1 and T2 Will increase, increasing the corresponding current flows in potentiometers 28 and 29. A part of the corresponding increased voltage drops across potentiometers 28 and 29 will be applied to the bases of transistors TPl and TP2, respectively, making these power transistors conduct. The emitter-base voltages of the power transistors in response to detection of a fire will be more than sufiicient to produce a voltage in the squib circuit in excess of the breakdown voltage of diode 35.

Conduction of power transistors TP1 and TP2 will produce an operating current in the series circuit including squib 33 and will cause squib 33 to explode. Squib 33 is operatively associated with a valve 36 interposed in a water (or other extinguishing medium) supply line 37. The squib 33 is arranged when exploded immediately to open valve 36 and thereby allow the high fluid pres sure upstream of the valve 36 to become effective downstream of the valve. The downstream portion of pipe 37 is primed with Water (or other medium) at a low pressure, the water being retained by a plug or cap 38. As soon as valve 36 opens, the high pressure becomes effective to force open the discharge end or nozzle of the pipe 37 by blowing out or pivoting the cap or plug 38, allowing the water to be discharged onto the hazardous area thereby to extinguish the fire. The valve 36, the primed pipe and the provision of the plug or cap 38 form no part of the present invention.

Should ambient light, as from a glint reflected from the surface 20, contact either photocell P1 or photocell P2, but not both, the current through potentiometer 28 or potentiometer 29, as the case may be, may be raised to a level at which the corresponding power transistor will be conditioned to conduct. However, since transistors TP1 and TF2 are connected in an AND gate, both must be conditioned to conduct before the squib circuit will be complete. Hence, such a stray light beam contacting one but not both of the photocells cannot act to discharge the extinguishing medium onto the hazardous area. The disposition of the photocells P1 and P2 angularly downward onto the same field of view makes the possibility of a glint of light or other stray beam contacting both photocells remote. Thus, each of the photocells is arranged to see essentially only the protected area and external illumination impinging thereon can come, as a practical matter, only from the protected area. But a light beam from a remote source reflected from the protected area is not likely to contact both photocells. On the other hand, since both photocells have the same field of view, i.e., the surface 20, a fire occurring on this surface will cast energy onto both photocells and hence will reliably operate the system.

Since any change in illumination acting on the photocells will tend to alter the current through the corresponding potentiometers 28 and 29, these potentiometers should be set so as to produce the desired emitter-base voltages on the corresponding power transistors. It will be evident that the potentiometers 28 and 29 are effectively gain or sensitivity controls, since the higher the setting of a potentiometer the lower will be the incident light energy necessary to operate the corresponding power transistors. The selection of diode 35 (or a number of such diodes connected in series) creates a threshold voltage in the power transistor emitter-base circuits below which conduction of the power transistors in the squib circuit cannot occur.

The valve 36 may be of any convenient type. For example, it may of the type in which the valve is opened upon motion of a short-travel plunger actuated by motion of a spring-urged arm and in which the arm is normally restrained by a frangible link arranged to be broken by the squib 33 when the latter is exploded.

Depending upon the valve construction and size, the squib 33 may be what is technically called a primer. And more than one squib or primer may be used if needed, the same being connected in parallel.

Since the switching time of solid state elements is very small and the speed of light very great, the operating voltage will appear across the squib terminals virtually instantaneously upon the occurrence of a fire condition in the protected area which will actuate the photocells, the actual time required being of the order of 5 to microseconds. The operation of a typical squib or primer is also very rapid. For example, a typical primer may have a firing time ranging from 1.2 milliseconds at a current of 200 milliamperes to 0.1 millisecond at 500 milliamperes. The power transistors TF1 and TF2 are preferably arranged to produce an operating current in the squib circuit near the high end of the squib or primer rating. The opening time of a properly designed valve is likewise small so that if the downstream water delivery pipe is primed and the upstream pipe is maintained at a suitable high pressure, water can be delivered to the protected area in an extremely short time after the occurrence of a visible fire condition. By operating the squib or primer at or near its high current rating, the time interval is reduced for practical purposes to the valve opening time. Hence, water can be delivered to the fire area in a time of the order of a few milliseconds. Such rapid response will not be needed for some hazards, but for others a respouse in such a short time interval will be of extreme importance.

It will be observed that the squib operating voltage is applied to the squib in FIG. 1 without the interposition of a relay. Since even a sensitive relay has an appreciable operating time, e.g., 5 to 10 milliseconds, it is desirable that relays or similar devices not be used so that the time delay will be reduced substantially to the inescapable minimum of the valve opening time. By making the squib a part of the valve mechanism, this time is reduced to a very small value.

Since spurious ignition of the squib, though unlikely, is possible (especially if the squib should be defective), the squib is preferably located some distance away from the protected area, e.g., 20 feet. In this way spurious ignition of the squib will not tend to ignite the hazardous material. By using a primed pipe downstream of the squib controlled valve, little time delay results from this separation.

Referring now to FIGS. 3, 4 and 4A, there is shown a modified form of fire detector in accordance with the invention. The construction of FIGS. 3 and 4 is similar to that of FIGS. 1 and 2, but whereas FIGS. 1 and 2 show a single fire detector unit comprising two fire detecting elements P1 and P2, in FIGS. 3 and 4 there are three fire detecting units each comprising a pair of fire detecting elements. Photocells P1 and P2 form one pair of fire detecting elements, photocells P3 and P4 form another pair of fire detecting elements, and photocells P5 and P6 form the third pair of detecting elements.

As shown in FIG. 3, photocells P1, P3 and P5 are connected in parallel with each other in a circuit position corresponding to that of photocell P1 in FIG. 1. Similarly, photocells P2, P4 and P6 are connected in parallel with each other in a circuit position correspond ing to that of photocell P2 in FIG. 1.

In FIG. 4 the hazardous area or zone is the interior of a mixer 39 having a material surface 40. The material in the mixer is agitated and mixed by a pair of paddles 41 and 42 rotated by shafts 43 and 44, respectively. The mixer 39 may comprise a removable mixing bowl 45 adapted to fit beneath a mixer body 46.

Brackets 47, 48 and 49 extend through holes in mixer body 46 located above the surface 40 and are spaced at 120 intervals. Bracket 47 carries photocells P1 and P6, bracket 48 carries photocells P5 and P4, and bracket 49 carries photocells P2 and P3. The photocells are inclined downwardly to yield fields of vision generally elliptical in shape (in a horizontal plane), as shown in FIG. 4A. However, portions of the ellipses are cut off by the mixer wal s.

The field of vision of photocell P1 is indicated by lines 59 and 51 yielding elliptical area 52 at surface 40 (FIG. 4A). Photocell P2, which views the same elliptical area 52 as photocell P1, has a field of vision indicated by lines 53 and 54. Photocells: P3 and P4 have fields of vision indicated by lines 55-56 and 57-58, respectively, and jointly view elliptical area 59 (FIG. 4A). Photocells PS and P6 have fields of vision indicated by lines 60-61 and 6Z63, respectively, and jointly view elliptical area 64 (FIG. 4A).

Basically, each pair of photocells Pl-Z, P34, and P5-6 is intended to View a respective segment of the surface 40. However, since the shafts and paddles obscure portions of the surface 40 as viewed by any individual photocell, the fields of view are somewhat enlarged to provide overlapping, as shown in FIG. 4A. By means of this overlapping, it can be assured that each individual portion of surface 40 will be viewed at all times by at least one of the even numbered photocells and also by at least one of the odd numbered photocells. For example, if a portion of the surface 40 normally in the field of View of photocell P1 is temporarily or permanently masked from this photocell by the paddle 41 or the shaft '7 43, such masked portion will be viewed by one or both of photocells P3 and P5.

In general, it is desirable that the field of view of each photocell be relatively limited and that no more overlapping of these fields than necessary to avoid blind spots be provided. Such limitation will minimize the likelihood of a spurious alarm. Thus, where appropriate, masks or other field limiting means may be provided in association with the photocells so that each will see its intended protection area but little or nothing outside of this area.

In the arrangement shown in FIG. 2, there is nothing to create blind spots, so two photocells are adequate to provide proper coverage of the hazardous area. Of course, if the hazardous area were large additional pairs of photocells could be used, as in FIG. 4, to limit the working area assigned to each pair of photocells.

With the relatively simple paddle and shaft mechanism of FIG. 4, three pairs of photocells can be arranged to prevent blind spots and so that there is no portion of the hazardous area that is not viewed at all times by at least one odd numbered photocell and at least one even numbered photocell. Should the elements tending to produce blind spots present a more complicated masking situation or should the hazardous area be large, a larger number of pairs of photocells may be used. It will be observed that the individual photocells of each pair, e.g., P1 and P2, view their common areas from opposite directions, as in FIG. 2.

As shown in FIG. 3, the even numbered photocells are connected in parallel with each other and the odd numbered photocells are connected in parallel with each other. The photocells PC1 and PC2 (not shown in FIG. 4) replace the resistors 26 and 27, respectively, of FIG. 1 and are disposed so as to receive ambient light only and are shielded from the hazardous zone so that they will not receive light energy from a fire in that zone.

The photocells PCI and PC2 should be arranged so that they are substantially equally affected by any changes in ambient light and so that this effect is substantially the same as that affecting the fire detecting photocells as groups, i.e., P1, 3, 5 and P2, 4, 6. Should it prove difilcult in any case to have a change in ambient light result in about equal resistance changes for a group of detecting photocells and the corresponding compensating photocell, two or more compensating photocells may be connected in parallel. Since changes in ambient light affect both the detecting and compensating photocells about equally, such changes in ambient light will produce little or no net change in the emitter-base voltages of the transistors T1 and T2, and hence will not tend to render the power transistor TP1 and TP2 conductive. A similar compensating effect is provided with respect to changes in ambient temperature. Resistance elements could be used in place of the compensating photocells, as in FIG. 1, if desired, for example, Where changes in ambient light level are not a serious problem.

Light from a fire contacting any one or more of photocells P1, P3 and P5 (which light will not contact photocell PC1) will increase the emitter-base voltage of transistor T1 and in turn increase the voltage drop across potentiometer 28, conditioning power transistor TP1 to become conductive, as described in connection with FIG. 1. Similarly, light from a fire contacting any one or more of photocells P2, P4 and P6 will condition power transistor TP2 to become conductive. When both power transistors are thus conditioned (and when the emitter-base voltages are sufficient to overcome the threshold value imposed by diode 35), current will flow in the squib circuit and squib 33 will be fired, as in FIG. 1. Thus, for the squib to be fired requires at least one photocell from each of the odd and even numbered groups of detecting photocells to view the fire. In most cases this would be corresponding photocells of a detector unit, e.g., P1 and P2 or P3 and P4. But should the fire occur '8 in the P1 segment of the surface 40 but be masked from P1, then the fire would be viewed by P3 and/or by P5, satisfying the AND gate requirement that at least one photocell of each detecting group view the fire.

FIG. 5 illustrates another single fire detecting unit arrangement. However, the arrangement of FIG. 5 differs from that of FIGS. 1 and 3 in that the fire detecting unit is formed from a multiple number of detecting elements. As shown, there are n detecting photocells P, n compensating photocells PC, n transistor amplifiers T, and 11 power transistors TP. The circuit operation is the same as that previously described except that the AND gate formed by the power transistors TP requires all n detecting photocells to detect a fire condition before the squib circuit will be energized.

It will be appreciated that where n is greater than two, the likelihood of a spurious alarm is decreased below the level afforded by the arrangement of FIG. 1. On the other hand, where n is greater than two, the danger that a fire may not be detected immediately is somewhat increased. To overcome this it may be desirable to con nect certain of the detecting photocells in parallel, as in FIG. 3, and yet provide each detecting unit with more than two photocells, as in FIG. 5.

Another arrangement which may be used in place of parallel connected detecting photocells is to connect certain of the power transistors in an OR gate while maintaining the squib circuit as a whole in the configuration of an AND gate. Such an arrangement is illustrated in FIG. 5A, in which power transistors TP1, TP2 and TPn3 are connected in series and power transistors TPn-2, 'I'Pn-Ll and TPn are connected in series, the series combinations being connected in parallel. With this arrangement, the squib circuit as a whole is an AND gate, but the AND condition may be satisfied by either TP1, TP2, and TPn-3 or T Pn-2, TPn-l, and TPn.

As shown in FIG. 5, optical filters F may be provided in associatiion with each of the detecting photocells. The filters F are disposed between the respective photocells and their corresponding segments of the hazardous area to allow the predominant spectral energy frequencies of the protected hazard to pass, but to minimize passage of other frequencies.

The filtering action is illustrated in FIG. 5B, which is a plot of wave length in microns versus relative response. In FIG. 5B, curve 65 represents typical response of a human eye, curve 66 represents typical response of a cadmium selenide photoconductor, while curve 67 represents the energy passing response of the filters F. From FIG. 5B it will be seen that the cadmium selenide photoconductor response peaks at about 0.75 micron, while the filter F cuts off energy below about 0.7 micron. Since visible light energy lies generally below about 0.7 micron, it will be evident that visible light beams will not be likely to cause spurious operation of the system.

While protection of the type contemplated by the inventlon can be provided on a continuous basis, in many cases protection will be required only while a hazardous operation is being conducted. For example, while hazardous materials are being mixed or While a shaping operation is being performed, e.g., a cutback operation, the danger of fire is acute and protection is required. Whether protection is required on a continuous basis or only during spaced intervals, testing of the system integrity and operability is important.

Considerable advantage can be secured in combining the testing and detecting elements. For example, in this way it can be ensured that the testing operations are uniform and that a desired test sensitivity is achieved. Moreover, testing in this manner can be performed just before a hazardous operation is commenced but without creating an additional hazard such as would occur in operating electrical equipment in close proximity to the hazardous material.

Referring now to FIG. 6, there is shown a combined detecting and test element having a housing 70 which may (but need not) be cylindrical in shape and which has an upper portion 71 made of transparent material and a lower portion 72 made of opaque material. For example, the upper portion 71 might be made of Lucite (methyl methacrylate), while the lower portion 72 might be made of Bakelite. The outer end of the transparent upper portion 71 has a circular opening 73 with tapered walls 74 (forming a frusto-conical section). The conical walls 74 are polished windows. The base of the opening 73 itself has an opening accommodating an opaque cylinder 75 open at its upper end and closed at its bottom end and holding a photocell 76, e.g., a cadmium selenide cell. The photocell 76 is preferably movable axially within the cylinder 75 to adjust the field of vision of the photocell. This field of vision will be conical in shape (for a circular light sensitive surface) and will be greatest when not restricted by the walls of the cylinder 75 or of the cone 74. By moving the photocell inwardly, the cylinder walls form a mask which limits the field of vision. As the photocell is moved outwardly the conical surface 74 acts as a field limiting mask, the masking effect being diminished as the photocell approaches the opening 73. Electrical leads 77 and 78 extend outwardly through the upper and lower portions 71 and 72, as shown, to afford electrical connection to the photocell. The cylinder 75 may be made of any suitable material, e.g., brass or Bakelite.

The lower portion 72 of the housing 70 has a cylindrical hollow space 79 in one end thereof, and the hollow space 79 communicates with a hollow well 80 housing a test lamp 81 and socket 82. Power leads 83 and 84 extend outwardly from the socket 82. The lamp 81 is designed to produce illumination having spectral characteristics resembling as closely as possible the spectral characteristics of the hazard which the photocell 76 is to protect. For example, for a cadmium selenide photoconductive element, the lamp 81 should produce primarily infrared energy.

Light from the lamp 81 travels through the space 79, as shown by the arrows 85, and through the transparent housing portion 71, as shown by the arrows 86. The outer end of the housing portion 71 is provided with an annular metallized reflecting surface 87 which reflects the light from lamp 81 incident thereon, a portion of this reflected ligh passing through the conical walls 74 and contacting the light-sensitive surface of the photocell 76, energizing the latter in the manner of a detected fire. By adjusting the intensity of the lamp 81, the photocell output resulting from operation of lamp 81 may be caused to match the desired sensitivity of the detecting system.

It will be observed that should dirt or other matter obscure the photocell 76, light from lamp 81 will be blocked from the photocell to the same extent as would light from a fire, and hence if such obscuration were sufficient to reduce materially system sensitivity, the illumination of lamp 81 would not yield a test signal representing a successful test.

The detecting and test element of FIG. 7 is similar to that of FIG. 6 except that two test lamps 81 and 81' are provided, the lamp 81 having a socket 82' and leads 83' and 84'. The hollow space 79 is omitted and the lamps 82 and 82' are mounted in wells 88 and 89, respectively, each having an open end communicating with the transparent portion 71. A filter 90 is mounted above the photocell 76 so as to be in the path of spectral energy entering the opening 73 or passing through the conical walls 74 and impinging on the photocell 76.

The detecting and test element of FIG. 8 is similar to that of FIG. 7 except that the upper end of the transparent housing portion 71 is frusto-conical in shape except for an inner annular ring surrounding the opening 73. This conical upper end and annular ring are provided with the metallized reflecting surface 87 which, as

10 in FIGS. 6 and 7, reflects test light through the polished window 74 but limits incident light from the hazardous area to the opening 73. The filter is omitted in FIG. 8.

FIGS. 9 and 10 illustrate still another form of combined detecting and test element in accordance with the invention. This element comprises a rectangular opaque housing 91 carried on a mounting bracket or nipple 92. The housing 91 has mounted therein a photocell 76 which is axially movable and may be locked in a desired position by a locking screw 93 acting in a threaded hole provided in the housing 91.

The housing 91 has a recess 94 in one end thereof extending over somewhat more than half the end surface of the housing. The photocell 76 is mounted beneath this recess and beneath filter 90 which covers a hole in the housing for passage of light to the photocell 76. The filter 90 is affixed to the bottom of the recess 94 by screws 95 acting in threaded holes provided in the recess bottom. A screw 96, also acting in a threaded hole provided in the bottom of the recess 94, serves as a convenient handle for adjusting the axial position of the photocell 76. For this purpose, the photocell is arranged to move with the recess bottom and the latter is axially slidable in the housing. When the desired photocell axial position is achieved, the screw 96 may be removed.

Light from test lamp 81 passes through a window 97 into the recess 94 above the filter 90. The side edge of the filter 90 is preferably opaqued or shielded so that light from lamp 81 can reach photocell 76 only through the upper surface of filter 90 and hence through the same path as light from a fire.

It will be observed that the walls of recess 94 afford a pentagonal mask for the photocell 76 and hence the field of view of photocell 76 will be generally pentahedral in shape.

In certain explosive atmospheres it may be hazardous to introduce any electrical power carrying wires and components which are not completely shielded. For operation under these circumstances, light-conducting tubes may be used, e.g., of the rigid plastic variety or the flexible fiber variety. Again, metallic tubing with polished metallized or electroplated walls may be used for light conduction.

A combined detecting and testing element in accordance with the invention and having all electrical connections shielded or remote from the hazardous area is illustrated in FIGS. 11 and 12. In these figures a photocell 76 is mounted partially within a recess in one end of a light-conducting rod or tube 98, this end of tube 98 being slidably mounted in a metal tube 99. Locking screws 100 are provided to lock the tube 98 and photocell 76 in a desired axial position. The end of the tube 99 may be threaded as shown at 101 for easy attachment to a mounting bracket.

A light-reflective coating 102 is provided about that portion of the tube 98 which extends outside of the tube 99, e.g., an aluminum foil wrapping. Such a coating affords the multiple reflections which provide superior light conductance axially of the tube 98. A protective opaque tape 103 is provided around the foil 102. The coating and tape would not be used where the tube itself is opaque. The rod or tube 98 may be curved in any desired manner for convenient exposure to the hazardous area, the end 184 of this tube or rod serving as the lightadmitting surface. Where this element 98 is a hollow tube, it is desirable that the light-admitting end he closed by a transparent window to prevent contamination of the tube walls.

A metal tube is mounted on the tube 98 and one end of the tube 105 overlies the light-admitting end 104 of the tube 98. The tube 105 contains a test lamp 81 and socket 82 and is provided with a window 106 from which light from lamp 81 may enter the end 104 of the tube 98. The end of tube 105 should be closed to prevent any exposure of the hazardous area to a possible spark from the electrical connections. If desired, the tube 105 may be light conducting and the lamp 81 may then be located at a point remote from the hazardous area.

A detecting and test circuit in accordance with the invention is illustrated in FIG. 13. In this circuit the detecting photocells P1-P6 and the transistor amplifiers T1 and T2 are connected as shown in FIG. 3. However, the compensating photocells are replaced by the resistors 26 and 27 of FIG. 1. The squib circuit is more complicated than has been shown in previous figures and extends from negative terminal 24 through front contacts 8T1-1 of a squib test switch ST, conductor 32, squib 33, conductor 34, microswitch contacts M, contacts TSl-l, T82-1 and TS3-1 of test switches T81, T82 and T83, respectively, contacts T'8G11 of general test switch TSG, the collector-emitter circuits of power transistors T P1 and TF2 and rectifier 35 to positive terminal 25.

Each of the detecting photocells is provided with a test lamp which may correspond to the test lamps of FIGS. 6-12 or be otherwise suitably disposed for test purposes. These lamps are designated TL1, TL2, TL3, TL4, TLS and TL6 and are operatively associated with photocells Pl-P6, respectively. The test lamps are divided into three pairs, the lamps of each pair being connected in series and the pairs being connected in parallel. The lamps corresponding to the detecting photocells which view the same fields of the hazardous area (FIGS. 4 and 4A) form the pairs. Thus lamps TL1 and TLZ, TL3 and TL4, and TLS and T116 form the respective pairs.

The free terminal of each of lamps TL1, TL3 and TLS is coupled to negative terminal 24 through contacts TSG-2 of switch TSG and a potentiometer T8. The free terminals of lamps TL2, TL4 and TLd are connected to positive terminal 25 through respective contacts TS1-2, TS22 and TS3-2 of switches T81, T82 and T83 respectively.

The source of potential for the system, here shown as a bat-tery 'B, is connected to terminals 24 and 25 through contacts MS1 of a main switch MS. Contacts MS2 of switch MS supply battery power to a lamp MD through a circuit including contacts T8G31 of switch TSG. Lamp ML might conveniently be green since its illumination signifies a protection-on or in-service condition. Upon operation of general test switch TSG to its test position, lamp ML will be extinguished and lamp TL will be illuminated, the circuit for the latter including contacts MS-2 and contacts T8G32 of switch TSG. Contacts TSG-3-1 and TSG-3-2 share a common armature. Lamp TL might conveniently be amber in color.

Contacts TSG-l-Z of switch TSG (which share a common armature with contacts TSG-l-l) are provided to complete the power transistor circuit to negative terminal 24 through an operating coil 81 of a relay or stepping switch S and a lamp RL instead of squib 33. Lamp RL might conveniently be red in color.

Contacts ST12 of switch ST (which share a common armature with contacts ST-l-l) are provided to connect one terminal of squib 33 to negative terminal 24 through a voltmeter V. Contacts ST-2 of switch ST serve to connect the other terminal of squib 33 to positive terminal 25.

The switch contact positions shown in FIG. 13 are for the protection-on condition and hence the protection-on or in-service lamp ML will be illuminated. Should a fire be detected by any one or more of photocells P1, P3 and P and also by any one or more of photocells P2, P4 and P6, squib 33 will be fired as previously described.

Switch M provided in the squib operating circuit might be a microswitch or the like arranged to be closed automatically when the mixing bowl or other apparatus is in position, thus preventing accidental firing of the squib in the absence of a hazard to be protected.

When it is desired to test the system, switch TSG will be operated. When apparatus such as the mixer of FIG.

4 is being protected, such testing should be undertaken before the mixer or other equipment is started, i.e., before the hazardous operation is commenced.

Upon operation of switch TSG, contacts TSG-L1 open and contacts TSG1-2 close, breaking the squib operating circuit and connecting red response lamp RL to positive battery through the power transistors TPl and TP2. Contacts T8G2 close connecting negative battery to test lamp pairs TL1 and 2, TL3 and 4 and TLS and 6. Contacts TSG31 open extinguishing green lamp ML and contacts TSG-32 close illuminating amber test lamp TL.

Each pair of detecting photocells may now be tested sequentially by operating and then releasing, in sequence, test switches T81, T82 and T 83. Operation of switch T81 completes the power circuit for test lamps TL1 and TLZ by closing contacts T81-2. The illumination provided by test lamps TL1 and T-L2 simulates an actual fire condition in the field of view of photocells P1 and P2, causing a response by these photocells and a corresponding response by transistors T1 and T2 and by power transistors TPl and TP2. Proper operation of these elements will cause squib operating current to flow through lamp RL, illuminating the latter as a visual signal of a satisfactory test. Subsequent operation of switches T82 and T83 will cause test lamps TL34 and TL'56 to test the operation of the corresponding photocells and to illurninate lamp RL twice more if a satisfactory test is achieved in each case.

It may be desired automatically to prevent operation of the mixer or other apparatus until the tests have been completed satisfactorily. For this purpose operating coil 81 of relay or stepping switch 8 is connected in series with lamp RL. The squib operating current flowing through coil 8 advances the relay or switch armature by one step. Three such steps are required however to close contacts 81-1 which are included in the operating circuit of the mixer motor. Holding .coil S2 is provided so that when main switch MS is operated to disconnect battery power at contacts MS1, relay or switch S will reset to zero count and open contacts 81-1. The three surges of squib operating current through coil 81 required to close contacts 81-1 are achieved by successive operation of switches T81, T82 and T 83 accompanied by successful tests of the corresponding photocells and apparatus. Coil 81 may be made sufiiciently sensitive as not to operate on a marginal current in the squib operating circuit so that even though lamp RL may be illuminated three times as required, contacts S11 will not close unless a satisfactory level of squib current fiow is achieved on each of the three tests and hence the hazardous operation cannot -be commenced.

The switch contacts TS11, TS21 and TS3-1 provided in series with squib 33 provide redundant protection (in view of contacts TSG-2) against accidental firing of the squib on operation of any of switches T81, T82 and T83. Integrity of the switch contacts in series with the squib operating circuit, including switch M, may be assured by momentarily operating a switch 83. Contacts 83-1 of switch 83, when closed, complete a circuit extending from negative battery .through the various switch contacts in the squib circuit, contacts 831, a current limiting resistor SR and a lamp SE to positive battery. Lamp SB, which might conveniently be blue, when illuminated shows integrity of the contact portion of the squib operating circuit. To guard against interference with squib operation through switch S3 accidentally being left in operated condition, contacts 83-2 are arranged to open the circuit of the mixer motor when switch S3 is operated. The lamp 83 should, of course, not draw sufficient current to fire the squib.

Potentiometer TS in the test lamp circuit provides a test sensitivity control. For this purpose the slider of potentiometer T8 is connected so as to permit variation of the current fiow to the test lamps. By varying this cur- 1? rent to the test lamps and observing the current level at which detection occurs as indicated by illumination of lamp RL, the sensitivity characteristics of the individual detecting photocell pairs may be ascertained. This determination affords a quantitative measure of system sensitivity in addition to the qualitative determination afforded by illumination of lamp RL and stepping of switch S.

Testing of squib integrity is afforded by operation of switch ST. This operation opens contacts ST11, closes contacts ST12 and closes contacts ST-Z. Squib 33 and voltmeter V are thus connected in series between negative and positive battery. Displacement of the voltmeter needle affords a quantitative determination of squib condition. The high impedance afforded by voltmeter V, like that afforded by resistor SR, limits the test current through the squib to a value insufficient to fire the squib. This test is to some extent redundant to that afforded by operation of switch S3. However, the test effected by operation of switch ST requires switch TSG to be in its test position, while switch S3 may be operated to effect a test with switch TSG in normal detection position. Contacts S33 of switch S3 may be included in series with in-service lamp ML to prevent illumination of the latter with switch S3 operated.

Since the squib circuit integrity test afforded by operation of switch S3 may be effected with the circuit otherwise in detecting condition, operation of switch S3 is preferably the last test. In this way proper closing of contacts ST-l-l, M, TSl-l, TS21, TS3-1 and TSG-14 is assured.

In FIG. 14 there is shown the face of a typical test panel showing lamps TL, RL, ML and SB, switches TSG, ST, MS, T51, T52, T83 and S3, voltmeter V and an additional lamp LP. Lamp LP, which may be associated with an audible alarm, is arranged to provide an alarm signal should pressure in the water line controlled by the squib operated valve fall below a predetermined safe level.

A removable shield may be mounted so as to prevent accidental operation of any of switches TSG, ST, T31, T82 and T83. A similar shield is shown for switch S3.

Switches TSl, TSZ, T83 and S3 may be spring loaded, self resetting push buttons, while switches MS, TSG and ST may be toggle switches of the break-before-make type.

When testing during a protection-on period is to be provided, it may be desired to simplify somewhat the test procedure so that protection is interrupted only while actual tests are in progress. For example, switch TSG may be omitted and protection will be afforded except during actual operation of switches TSl, T82 and TS3. Relay or switch S may be omitted since it will not generally be desirable to stop the hazardous operation while testing.

It may be sufiicient in some cases to effect testing by means of one or more lamps located in the hazardous area. In such case photocell pairs (or groups) other than a pair being tested, may be disabled so that system testing by pairs (or other groups may be achieved.

While the invention has been described in connection with specific embodiments thereof and in specific uses, various modifications thereof will occur to those skilled in the art without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. Apparatus for detecting the occurrence of a fire condition in a hazardous zone and for supplying an operating signal to a fire extinguishing mechanism, comprising a plurality of radiation detectors arranged so that radiation emanating from said zone will impinge thereon, said radiation detectors being oriented with respect to each other and with respect to said zone so that said detectors view said zone from respectively different angles, means coupled to said radiation detectors, said signalling means being arranged to produce said operating signal only when radiation having an intensity greater than a predetermined minimum value simultaneously impinges upon each of said radiation detectors, and means to supply said operat ing signal to said fire extinguishing mechanism.

2. Apparatus for detecting the occurrence of a fire condition in a hazardous zone and for supplying an operating signal to a fire extinguishing mechanism, comprising a plurality of radiation detectors arranged so that radiation emanating from said zone will impinge thereon, said radiation detectors being oriented with respect to each other and with respect to said zone so that said detectors view said zone from respectively different angles, a like plurality of individual signalling means each coupled to and controlled by a respective one of said radiation detectors, said signalling means being arranged electrically with respect to each other in AND gate relationship thereby to produce said operating signal only when radiation having an intensity greater than a predetermined minimum value impinges upon all of said radiation detectors, and means to supply said operating signal to said fire extinguishing mechanism.

3. Apparatus for detecting the occurrence of a fire condition in a hazardous place having a plurality of substantially symmetrical zones, comprising a plurality of groups of radiation detectors, each of said groups comprising a plurality of individual radiation detectors arranged with respect to said place so that radiation emanating from a particular zone will impinge thereon, the radiation detectors of each group being arranged with respect to each other so as to view the corresponding particular zone from respectively different angles, said different angles of view with respect to the corresponding zones being generally similar for all of said groups so that each individual detector has a correspondingly disposed detector in each group, said correspondingly disposed detectors in all of said groups forming sets of detectors, said zones overlapping sufiiciently so that a fire condition producing radiant energy at any point in said place will cause radiation to impinge on at least one detector of each set, a plurality of individual signalling means each coupled to all of the detectors of a respective set and arranged to be controlled by any of the detectors of the corresponding set, and means intercoupling said individual signalling means in AND gate relationship, each of said individual signalling means being arranged partially to condition said AND gate to produce an output signal when at least one of the detectors of the corresponding set receives radiation having an intensity greater than a predetermined value, said AND gate producing said output signal only when all of said individual signalling means are so conditioned.

4. Apparatus for detecting the occurrence of a fire condition in a hazardous place having a plurality of zones and for supplying an operating current to an explosively actuated fire extinguishing mechanism operatively arranged with respect to said place and having a. current operated explosive actuator, comprising a plurality of groups of radiation detectors, each of said groups comprising a plurality of individual radiation detectors arranged with respect to said place so that radiation emanating from a particular zone will impinge thereon, the radiation detectors of each group being arranged with respect to each other so as to view the corresponding particular zone from respectively different angles, said different angles of view with respect to the correspond ing zones being generally similar for all of said groups so that each individual detector has a correspondingly disposed detector in each group, said correspondingly disposed detectors in all of said groups forming sets of detectors, said zones overlapping sufficiently so that a fire condition producing radiant energy at any point in said place will cause radiation to impinge on at least one detector of each set, a plurality of individual signalling means each operatively associated with all of the detectors of a respective set and arranged to be controlled by any one of the detectors of the corresponding set, each of said individual signalling means comprising a power transistor having an output circuit, and an actuating circuit including, in series connection, said output circuits of said power transistors, a source of actuating potential and said current operated explosive actuator, said individual signalling means each being arranged to condition the corresponding power transistor to become conductive when at least one of the detectors of the corresponding set receives radiation having an intensity greater than a predetermined minimum value, all of said power transistors becoming conductive only when at least one detector of each set receives at least said minimum intensity radiation, said actuating circuit being closed when all of said power transistors become conductive thereby to operate said explosive actuator.

5. Apparatus as set forth in claim 4 comprising selectively operable means to supply to the radiation detectors of each of said groups radiation simulating the occurrence of a fire condition in the corresponding zone, and current responsive signal registering means, said selectively operable means being arranged when operated to disconnect said explosive actuator from said actuating circuit and to connect said signal registering means in said actuating circuit whereby said signal registering means registers current fiow in said actuating circuit in response to said simulated fire condition.

6. Apparatus for detecting the occurrence of a fire condition in at least a hazardous zone of a hazardous place and for operating a current responsive fire extinguishing mechanism, comprising a plurality of photocells each disposed so that substantially said entire zone lies in the effective field of view of each of said photocells, said photocells being arranged with respect to each other and with respect to said zone so that said photocells view said zone from respectively different angles, a like plurality of transistor amplifiers each coupled to a respective one of said photocells and each being arranged to have an output proportional to the intensity of radiation incident on the corresponding one of said photocells, a like plurality of power transistors each having an input circuit, said input circuits of said power transistors each being coupled to a respective one of the output circuits of said transistor amplifiers and being arranged to condition said power transistors to become conductive when the output of the corresponding one of said transistor amplifiers reaches a predetermined minimum value, and a signal output circuit including the output circuits of said power transistors, said output circuits of said power transistors being connected in predetermined AND gate arrangement in said signal output circuit whereby said signal output circuit is closed only when more than one of said power transistors are conductive in accordance with said gate arrangement whereby only radiation incident on a combination of said photocells which will satisfy said gate arrangement will result in closing of said signal output circuit.

7. Apparatus as set forth in claim 6, comprising a plurality of additional photocells each exposed to ambient illumination but shielded from said hazardous place, each of said additional photocells being coupled to the input circuit of a respective one of said transistor amplifiers and being arranged to oppose any change in input to the corresponding transistor amplifier caused by changes in ambient illumination impinging on the corresponding photocell disposed so as to view said zone.

8. Apparatus for detecting the occurrence of a fire condition in at least a hazardous zone of a hazardous place and for supplying an operating current to a current responsive explosively actuated fire extinguishing mechanism comprising first and second photoconductive elements arranged so that radiation emanating from said zone will impinge thereon, said first and second elements being oriented with respect to each other with respect to said zone so that said first and second elements view said zone from substantially opposite di- IeCtions, Signalling means coupled to said first and second elements, said signalling means being arranged to produce said operating current only when radiation having an intensity greater than a predetermined minimum value simultaneously impinges upon both of said first and second elements, and means including a signalling circuit to supply said operating current to said current responsive explosively actuated fire extinguishing mechanism.

9. Apparatus as set forth in claim 8 in which said signalling means comprises first and second solid state signal amplifiers having input circuits coupled to said first and second photoconductive elements, respectively, and first and second solid state power amplifiers having input circuits coupled to and being controlled by the output circuits of said first and second solid state signal amplifiers, respectively, the output circuits of said power amplifiers being connected in series as part of said signalling circuit.

10. Apparatus as set forth in claim 9, comprising third and fourth photoconductive element exposed to ambient illumination but shielded from said hazardous place, and a source of direct potential, said first and third photoconductive elements and said second and fourth photoconductive elements being connected, respectively, as voltage dividers across said source of potential, the input circuits for said first and second solid state signal amplifiers being coupled to said voltage dividers between said first and third photoconductive elements and between said second and fourth photoconductive elements, respectively.

11. Apparatus for detecting the occurrence of a fire condition in a hazardous place having a plurality of zones, comprising a plurality of groups of photocells, said photocells being arranged so that each of said zones lies substantially completely within the field of view of all of the photocells forming a respective one of said groups, the photocells of each group being arranged with respect to each other in angular disposition so as to view the corresponding zone from respectively different angles, said angular disposition of individual photocells within each group with respect to the corresponding zone being generally similar for all of said groups whereby each photocell of a group corresponds to a similarly disposed photocell of the other groups, said corresponding photocells forming a set, a plurality of transistor amplifiers each having an input circuit coupled to the photocells of a respective one of said sets and having an output proportional to the intensity of radiation incident upon the photocells of the respective set, a plurality of adjustable impedance elements, means to supply the output of each of said transistor amplifiers to a respective one of said impedance elements, a plurality of power transistors each having an input circuit coupled to a respective one of said impedance elements, and a signalling circuit including, in series connection, the output circuits of more than one of said power transistors and a source of signalling potential, said power transistors each being arranged to be conditioned to become conductive when the radiation incident on any of the photocells of the corresponding set reaches an intensity at which the output of the corresponding transistor amplifier reaches a predetermined minimum value, said power transistors having series connected output circuits becoming conductive to close said signalling circuit only when at least one photocell of each of the corresponding sets receives radiation having said intensity sufiicient to condition the corresponding power transistors to become conductive whereby radiation not incident on at least one of the photocells of any one of said corresponding sets will not result in the flow of current in said signalling circuit.

12. Apparatus for detecting the occurrence of a fire condition in a hazardous place having a plurality of substantially symmetrical zones and for supplying an operating current to an explosively actuated fire extinguishing mechanism operatively arranged with respect to said place and having a current actuated explosive actuator, comprising a plurality of groups of photocells, said photocells being arranged so that each of said zones lies substantially completely Within the field of view of all of the photocells forming a respective one of said groups, the photocells of each group being arranged with respect to each other in angular disposition so as to view the corresponding zone from respectively different angles, said angular disposition of individual photocells within each group with respect to the corresponding zone being generally similar for all of said groups whereby each photocell of a group corresponds to a similarly disposed photocell of the other groups, said corresponding photocells forming a set, means intercoupling the photocells of each set in parallel with each other, a plurality of voltage divider circuits each including a respective one of said sets of photocells, a plurality of transistor amplifiers each having an input circuit coupled to a respective one of said voltage divider circuits and having an output proportional to the intensity of radiation incident upon the photocells of the set included in the corresponding voltage divider, a plurality of adjustable impedance elements, means to supply the output of each of said transistor amplifiers to a respective one of said impedance elements, a plurality of power transistors each having an input circuit coupled to a respective one of said impedance elements, and an actuating circuit including, in series connection, a rectifier element, the output circuits of said power transistors, a source of actuating potential and said current actuated explosive actuator, said power transistors each being arranged to be conditioned to become conductive when the radiation incident on any of the photocells of the corresponding set reaches an intensity at which the output of the corresponding transistor amplifier reaches a predetermined minimum value, said power transistors becoming conductive to close said actuating circuit only when at least one photocell of each of said sets receives radiation having said intensity sufficient to condition the corresponding power transistors to become conductive whereby radiation not incident on at least one of the photocells of any one of said sets will not result in the supplying of current to said explosive actuator.

13. Apparatus for detecting the occurrence of a fire condition in a hazardous place having a plurality of substantially symmetrical zones and for supplying an operating current to an explosively actuated fire extinguishing mechanism operatively arranged with respect to said place and having a current actuated explosive actuator, comprising a plurality of groups of photocells, said photocells being arranged so that each of said zones lies substantially completely within the field of view of all of the photocells forming a respective one of said groups, the photocells of each group being arranged with respect to each other in angular disposition so as to view the corresponding zone from respectively different angles, said angular disposition of individual photocells within each group with respect to the corresponding zone being generally similar for all of said groups whereby each photocell of a group corresponds to a similarly disposed photocell of the other groups, said photocells corresponding to similarly disposed photocells of said other groups forming a set, means intercoupling the photocells of each set in parallel with each other, a plurality of voltage divider circuits each including a respective one of said sets of photocells, a plurality of transistor amplifiers each having an input circuit coupled to a respective one of said voltage divider circuits and having an output proportional to the intensity of radiation incident upon the photocells of the set included in the corresponding voltage divider, a plurality of adjustable impedance elements, means to supply the output of each of said transistor amplifiers to a respective one of said impedance elements, a plurality of power transistors each having an input circuit coupled to a respective one of said impedance elements, an actuating circuit including, in series connection, a rectifier element, the output circuits of said power transistors, a source of actuating potential and said current actuated explosive actuator, said power transistors each being arranged to be conditioned to become conductive when the radiation incident on any of the photocells of the corresponding set reaches an intensity at which the output of the corresponding transistor amplifier reaches a predetermined minimum value, said power transistors becoming conductive to close said actuating circuit only when at least one photocell of each of said sets receives radiation having said intensity sufiicient to condition the corresponding power transistors to become conductive whereby radiation not incident on at least one of the photocells of any one of said sets will not result in the supplying of current to said explosive actuator, an individual source of radiation for each or" said photocells, each of said sources of radiation simulating a fire condition in the corresponding zone, selectively operable switching means for sequentially emergizing said sources of radiation corresponding to the photocells of each group, and current responsive signal registering means, said switching means, when operated, acting to substitute said signal registering means for said explosive actuator in said actuating circuit whereby said signal registering means registers current flow in said actuating circuit in response to said simulated fire condition.

14. Apparatus as set forth in claim 13 comprising means to adjust the intensity of radiation provided by said individual sources of radiation through a range of values whereby operation of said signal measuring means provides a comparative indication of the fire detection sensitivity of said individual groups of photocells.

References Cited by the Examiner UNITED STATES PATENTS 2,099,764 11/1937 Touceda 340-228 X 2,207,097 7/1940 Logan 250-239 2,278,920 4/1942 Evans et al 340228 2,415,179 2/ 1947 Hurley 340-228 2,563,274 8/1951 Rendel 3402 14 2,577,973 12/1951 MacDougall et al. 340-228 2,621,239 12/1952 Cade et al 340228 2,631,247 3/1953 Shaw 250-239 2,897,485 7/ 1959 Johnson 340228 2,938,529 5/1960 Olson 1699 2,946,990 7/ 1960 Klein 340228 NEIL C. READ, Primary Examiner.

BENNETT G. MILLER, EVERETT W. KIRBY, LOUIS J. DEMBO, ROBERT H. ROSE, Examiners. 

1. APPARATUS FOR DETECTING THE OCCURRENCE OF A FIRE CONDITION IN A HAZARDOUS ZONE AND FOR SUPPLYING AN OPERATING SIGNAL TO A FIRE EXTINGUISHING MECHANISM, COMPRISING A PLURALITY OF RADIATION DETECTORS ARRANGED SO THAT RADIATION EMANATING FROM SAID ZONE WILL IMPINGE THEREON, SAID RADIATION DETECTORS BENG ORIENTED WITH RESPECT TO EACH OTHER AND WITH RESPECT TO SAID ZONE SO THAT SAID DETECTORS VIEW SAID ZONE FROM RESPECTIVELY DIFFERENT ANGLES, MEANS 